Cells infected with the filamentous bacteriophage fd (or M13) synthesize many copies of the protein coded for by the viral gene 8 as the 73-residue procoat protein with its 23-residue leader sequence. The procoat protein is inserted in the cell membrane where it is cleaved by leader peptidase to the 50-residue coat protein which is stored in the membrane prior to being assembled to form the virus particles. The procoat and coat proteins are among the most favorable experimental systems for biophysical investigations of leader sequences and membrane-protein interactions, since: they are small, can be prepared in large quantities, can be labelled with stable isotopes, can be altered by site-specific mutagenesis, and many results have been obtained from the on-going investigations. The structure and dynamics of the membrane bound forms of the coat protein and its precursor, procoat protein, will be described by solution NMR studies of these proteins in detergent micelles and by solid state NMR studies of these proteins in phospholipid bilayers. The procoat protein will be studied in aqueous solution as well. This research will provide detailed descriptions of the coat protein during several stages of the lifecycle of the virus, thereby contributing to the understanding of processes important to molecular biology, where the mechanisms of packaging of DNA by protein and the roles of leader sequence in controlling protein processing and compartmentalization are topics of intense current interest.